1. Field of the Invention
The present invention regards devices for handling pipes, especially devices for handling pipes in connection with petroleum production.
2. Description of the Related Art
In petroleum production, a large number of pipes is used for various purposes. When drilling a well, a total of up to several kilometres of drill pipes may be used, each of which pipes is generally approximately 10 m long. Prior to use, these pipes are stored in horizontal stacks on deck. The pipes are connected by threes to form so-called stands. During drilling, the pipes are stored vertically as stands in so-called finger boards on the drill floor, up along the derrick. During drilling, the entire drill string must be withdrawn from the well at certain intervals, so-called tripping, e.g. in order to change the drill bit. With today's technology, the pipes are inserted back into the finger boards in order to be easily accessible for future use.
Up to several kilometres of casing may also used in a well in order to form walls in the wellbore. In the same way, several kilometres of production tubing is used in order to recover oil and/or gas from the well. In addition, several kilometres of other types of piping would generally then be required, for instance injection piping. All these pipes must at some stage be stored on or near the rig.
Traditionally, the movement of pipes between the pipe rack and the drill floor has to a large extent been accomplished through manual work. This task is heavy and entails a great danger to life, health and materials. Great efforts have therefore been made to reduce the element of manual work and transfer this to machines, which are preferably remotely controlled.
One factor is decisive when it comes to the profitability of petroleum production, and that is time. As the equipment used is very expensive, the time it takes from when the equipment is put into service, i.e. the drilling is initiated, until the production starts, will to a large extent be decisive in the cost of the development. It is therefore of great importance to reduce the time consumption during all parts of the development. During the pipe handling processes, it is important to have all the pipes ready when they are to be run into the well, and also to ensure that they can be carried away quickly from the drill floor when they are retrieved from the well.
Furthermore, the fact that standing pipes or stands contribute towards giving the drilling or production installation a high centre of gravity, is increasingly becoming a problem. With the increase in drilling depth over the recent years, the number of pipes has increased considerably. Also, the use of smaller, floating installations such as drill ships has become increasingly common. A high centre of gravity in such installations causes instability. As such, it becomes difficult to satisfy the requirements for stability. This means that other equipment must be moved down, possibly also involving an increase in ballast. This leads to less flexibility in the utilisation of the available space. In the case of vertically stored pipes, the wind catchment area also increases, which in combination with a high centre of gravity may have fatal consequences. Thus it has long been desired to be able to store the pipes horizontally. This has however involved awkward and time consuming pipe handling.